This invention relates generally to the rendering of latent electrostatic images visible and, more particularly, to a developer apparatus including a toner metering and charging structure.
The invention can be utilized in the art of xerography or in the printing arts. In the practice of conventional xerography, it is the general procedure to form electrostatic latent images on a xerographic surface by first uniformly charging a photoconductive insulating surface or photoreceptor. The photoreceptor comprises a charge retentive surface. The charge is selectively dissipated in accordance with a pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves a latent charge pattern on the imaging surface corresponding to the areas not struck by radiation.
This charge pattern is made visible by developing it with toner. The toner is generally a colored powder which adheres to the charge pattern by electrostatic attraction. The developed image is then fixed to the imaging surface or is transferred to a receiving substrate such as plain paper to which it is fixed by suitable fusing techniques.
The development of images by various methods, including electrostatographic means is well known. In some of these systems, toner particles are deposited on an electrostatic latent image contained on an insulating surface, such as selenium, utilizing, for example, cascade development, magnetic brush development, powder cloud development, touchdown development, and the like.
In view of some of the disadvantages of two component systems, there has been considerable effort directed to designing systems which utilize only toner particles, for example, U.S. Pat. No. 2,846,333, which discloses a single component developer composition that is comprised of toner resins, colorants and magnetic materials. Many of the single component development systems contain conductive toner particles, whereby imagewise toner deposition onto the imaging member is obtained by induction charging of the toner particles. Electrostatic transfer of conductive toner particles to plain bond paper is, however, usually inefficient as the charge on the toner particles can be reversed by induction charging from the paper during the transfer step. Accordingly, electrophotographic systems wherein conductive single component toner particles are used require an alternative transfer method and materials such as a special overcoated insulating paper to achieve sufficient toner transfer. Furthermore, in single component systems with conductive toner particles, the control of undersirable background or background suppression cannot usually be achieved with electrostatic forces alone, as the toner particles are inductively charged and deposited on the imaging bearing member in both the image and background areas, which is not the situation in two component developer systems where suppression of background development is accomplished by electrostatic forces acting on the triboelectrically charged toner particles, causing such particles to be directed away from image bearing member.
Recent developments in the area of single component development has resulted in an efficient, economical, simple process and apparatus wherein insulative, non-magnetic, toner particles are appropriately charged and there is obtained two component image quality utilizing a single component development apparatus. In this system, as described in U.S. Pat. No. 4,505,573 issued on Mar. 19, 1985, the disclosure of which is totally incorporated herein by reference, a charging roll means simultaneously meters and charges toner particles. A donor electrode roll serves to transport the toner particles, which electrode can be comprised of numerous suitable materials including for example a conducting roll overcoated with a polymer containing carbon black.
Heretofore, one of the aforementioned rolls (i.e. charging roll or donor electrode roll) was fabricated so that it was compliant to accommodate the runout of the other roll which was rigid. Such compliant roll structures usually consisted of a thin metal, for example, an electroformed nickel, sleeve mounted on a foam core. Although such a structure is functional for its intended purpose, several disadvantages have been noted including difficulty of manufacture, susceptibility to damage, foam set and sealing reliability.
Certain patents which may be relevant to the present invention will now be discussed.
U.S. Pat. No. 3,143,438 issued on Aug. 4, 1964 relates to apparatus for coating web material. Disclosed therein is a metering and smoothing device comprising a cylindrical rod which is mounted between a flexible doctor blade and a rod holder or receiving member.
U.S. Pat. No. 3,245,377 issued on Apr. 20, 1962 relates to an apparatus for coating paper. Disclosed is a cylindrical rod which extends lengthwise of a resilient backing roll and is retained in a socket by spring pressure exerted by a spring clip.
U.S. Pat. No. 4,382,420 issued on May 10, 1983 relates to an apparatus for developing a latent electrostatic image formed on a photoconductive recording material in a dry type electrophotographic copying machine typically employing a one component type developer with a conductive electrode held in contact with the developer. The electrode is connected to a power source through a switching device and serves to charge the developer to a predetermined polarity with a predetermined potential before the latent image is developed. In this way, the latent image can be developed selectively as either a normal image or a reverse image quite easily. FIG. 6 thereof discloses a charge and metering roller which regulates the layer of toner on a development belt and serves as an electrode as well.
U.S. Pat. No. 4,459,009 issued on July 10, 1984 relates to a process and apparatus for charging insulating toner particles wherein there is provided a charging roll containing a triboelectrically active coating, and weakly charged toner particles are transported into contact with the coating contained on the charging roll, this contact being accomplished in a charging zone situated between the charging roll and the transporting mechanism. As a result of contact between the weakly charged toner particles and the triboelectrically active coating contained on the charging roll there is imparted charges of either a positive or negative polarity to the weakly charged toner particles. The apparatus and process of the present invention are useful, for example, in electrostatographic recording imaging devices.
U.S. Pat. No. 4,464,041 issued on Aug. 7, 1984 relates to developing apparatus for producing an electrostatic latent image on a charge retaining member such as a drum, a rotating member for producing a shifting magnetic field is used to transport magnetic toner on a stationary sleeve from a toner source to a developing area on the drum. The amount of toner so transported is regulated by a magnetizable member positioned adjacent the rotating member before the developing area, the magnetizable member being characterized by a curved surface on which a shifting magnetic field is induced by the said rotating member and which attracts excess toner from the latter.
U.S. Pat. No. 4,505,573 issued on Mar. 19, 1985 relates to an apparatus for effecting the charging of insulating toner on a moving roller, and a toner transporting roller or belt with a coating thereover comprised of a mixture of conductive particulate particles, such as carbon black. The coating may be textured with silica particles. Useful polymers selected for the coating include fluorinated ethylene-propylene and polytetrafluorothylene copolymers.
U.S. patent application Ser. No. 171,062 filed on or about Mar. 21, 1988 and assigned to the same assignee as the instant invention discloses a scavengeless development system in which toner detachment from a donor and the concomitant generation of a controlled powder cloud is obtained by AC electric fields supplied by self-spaced electrode structures positioned within the development nip. The electrode structure is placed in close proximity to the toned donor within the gap between the toned donor and image receiver, self-spacing being effected via the toner on the donor. Such spacing enables the creation of relatively large electrostatic fields without risk of air breakdown.